For those new to comics as a medium, I suggest exploring your ideas as a short comic first, before diving into your epic. 8 page self contained mini, 4koma strips, whatever format you want to play around with, but get to know your characters first. From there, I suggest narrowing it down to just ONE idea, ONE audience, you really want to create for (and yes, you count as an audience), and then write a synopsis of your story. Before you begin actively working on it, you should know how it it ends- that'll help you figure out how to get there, and give you a concrete ending to work towards.
Know Your Medium:
From there, how you break down the comic work is up to you and your preferences, as well as your intended format. Do you want a print comic? A webcomic? Do you want to have a huge buffer before you begin sharing it because you work a dayjob? Knowing your limitations, and what you want the end result to be, will help you plan your comic project from the get go.
Even the differences between hosting the comic yourself, and sharing it to Webtoons or Tapastic will mean different formats. Platforms such as Tapas and Webtoons prefer vertical scrolling comics, self hosted comics traditionally display one page at a time, with forward and back buttons for navigations. Webcomics and comics for print have different pacing- even how frequently you update your webcomic will effect how you plan. Webcomics, when consumed by an up to date audience, are read one page at a time, one update at a time, whereas print comics are consumed as an entire issue (24 pages) or as a trade (24+ pages). In terms of pacing, this can mean the difference between a cliffhanger every 10 pages or so, or on every page.
Digital art, traditional art, watercolor, inks- your medium of choice will affect your process, as well as your timeline. Only you can determine which media is right for your project, and I recommend trying a variety before settling on one. Over time, digital art may prove more economical- you invest in a new computer once every half decade, whereas with traditional media, you're currently investing in new materials. However, working traditionally means you can possibly sell your finished originals to collectors.
Writing and Planning:
In terms of writing there are loads of ways to plot your story- some people prefer to write by the seat of their pants, some prefer to have it plotted out. Some want to work within the three act structure, and use the hero's journey as a format, some want to write slice of life gag strips- all of those have different writing considerations. One of my favorite methods for planning a story is utilizing a beat sheet to keep action and story moving along smoothly.
I find it helpful to start with a synopsis of my story- a beginning, a middle, and an end, and script around that. Knowing where I want my story to go helps me get it there.
Know Your Artist:
If you're writing for someone else, or if future you has a bad memory, I've found that a tight script, that includes shot choices and stage directions, works best for me and the types of comics I create, but every creator differs, and it's best to know what works for your artist (even if you're the artist- be honest with yourself). A lot of comic creators have a loose outline, and do their best storytelling in thumbnails.
Know Your Audience:
Writing for kids is very different from writing for adults, or even for teenagers. Knowing your audience will help you decide how to best tell, and present your story.
Show, Don't Tell (but sometimes explain)
Instead of relying on walls of text and verbal exposition, try to show your characters going through it, or better yet, dealing with the consequences.
When dealing with cultural comics, exposition dumps can be important, because you're explaining a culture to an audience that's unfamiliar with it. so a cultural comic, even if it's fictional, has an element of non fiction- a real culture that people care about
When creating a new world, you need to get your audience to care about that setting or at least the characters, before you try to dump a lot of worldbuilding information. In this case, worldbuilding should be integrated into the fabric of the comic whenever possible.
Great ways to dump exposition:
Bonus 4Koma strips
Character Q&A pages
A story/concept bible
Practice Makes Perfect:
I did the math last night, and my first five comics (and all but the very first had 100+ pages finished art and lettering) never saw any real audience outside my tight knit friend group. I did a strip comic, a gag a day comic, a 4 koma, and two sequential story comics just because I loved the medium and wanted to participate in it, but wasn't comfortable sharing and didn't have a community to share TO. Even when I was ready to start sharing my art, I did so in a very limited form- several short, 10 page comics (Ahoy, Foiled, Momotaro) and anthology pitches.
Although my work is still far from perfect, putting the time in, making comic pages, and practicing comics as a storytelling platform has allowed me to improve my craft. The more comics I make, and the more types of comics I experiment with, the better I'll be able to express my ideas in a comic format. The only way you can get better at making comics is to MAKE COMICS.